The invention relates to apparatus in which the speed of a double-acting pneumatic cylinder is adjusted for each travel direction by means of a unidirectional flow limiter placed between the orifice of the pressure cylinder through which the air escapes during the adjusted stroke and its directional control valve. Such an apparatus, also called adjuster, comprises an adjustment screw fast with a needle-valve for limiting at will the flow of air escaping through its seat which thus determines the speed of the cylinder. So that, in the other travel direction, the drive fluid is admitted at full flow into this same chamber, the adjuster further comprises a unidirectional valve opening in the direction of the intake flow and closing in the direction of the escape flow. Conventional adjusters only allow a single adjusted speed for one travel direction of the pressure cylinder, which speed is established at the outset and remains constant. Now, in a large number of cases, it would be desirable to have, during each stroke and on demand, two speeds of different values, which would increase the operating rates while avoiding end of travel shocks, or else allowing a rapid speed of a tool to be readily obtained followed by a slower working speed.
The present invention makes it possible to attain this aim, by providing two-speed adjusters, the passage from one speed to a second adjusted lower speed being achieved by a pneumatic control signal arriving in the apparatus and the reverse operation by disappearance of this signal.
Various prior art arrangements are known including these as follows:
______________________________________ Adams 3,090398 Britain 2,032,581 France 2,343,280 (U.S. Pat. No. 4,214,607 and U.S. Pat. No. 4,171,007) France 2,363,015 (U.S. Pat. No. 4,287,812 and U.S. Pat. No. 4,192,346) ______________________________________
These patents or known prior uses teach and disclose various types of valve metering systems of various sorts and of various manufactures and the like as well as methods of their construction, but none of them whether taken singly or in combination disclose the specific details of the combination of the invention in such a way as to bear upon claims of the present invention.